The present invention relates to a papermaker felt having an improved seam, and more particularly relates to a papermaker felt, wherein the felt includes spaced, parallel extending monofilaments that are formed on the underside thereof and that provide protection for the seam and further define water channels for the expressing of water therethrough when the felt is used in a press section of a papermaking machine.
Prior to the instant invention, technology in papermaker felts has advanced to the point where the felts whether woven or endless, are so constructed that they may be separated prior to installation and then seamed together when mounted on a papermaking machine. Thus, conventional seamed felts provide a convenient manner of mounting the felt in place on the rolls of the papermaking machine without having to dismantle the machine as was conventional in the use of the heretofore known endless belt type of felt. Examples of papermaking felts that have their ends joined in a seam are illustrated in the following U.S. Patents: Draper U.S. Pat. No. 2,883,734; Kerber U.S. Pat. No. 3,653,097; Romanski et al U.S. Pat. No. 4,006,760; Lees et al U.S. Pat. No. 4,026,331; Dutt et al U.S. Pat. No. 4,123,022; MacBeau U.S. Pat. No. 4,438,789; Luciano et al U.S. Pat. No. 4,574,435; Lilya et al U.S. Pat. No. 4,601,785; Sarrazin et al U.S. Pat. No. 4,695,498; Talonen et al U.S. Pat. No. 4,698,250; Halker et al U.S. Pat. No. 4,761,329; Eschman U.S. Pat. No. 4,775,446; Legge et al U.S. Pat. No. 5,015,220.
One of the disadvantages of the conventional seam felt as known heretofore, is that the seam often leads to machine vibration problems in the seam area. Heavy roll nip pressure can accentuate any non-uniformity in thickness in the seam area that results in an unacceptable paper product. Another disadvantage is that the heavy roll nip pressures may create a bump in the non-uniform water flow pattern in the seam area, which could create a water dam and possibly break down the wet paper sheet as the seam passes through a hard nip. Still another disadvantage of the conventional seamed felt is that oftentimes paper stock will bleed through the seam area because of non-uniform water flow and overall porosity. Problems have also been experienced in the conventional seam felt in that the seam is inherently prone to excessive wear due to the fact that it may be protected only by a thin layer of fiber or flap which is usually loosely bound to the body of the felt. The flap may be penetrated with resin to effect stabilization and resistance to wear, but this could alter the porosity in the area or create great difficulty in the joining of the ends of the fabric. Conventional seam felts are also prone to impart a mark to the sheet due to non-support of the seam and non-uniform water flow, especially later in the life of the felt when the protective flap has been worn away.
It is also known, as illustrated in the U.S. Patent to Jamieson U.S. Pat. No. 3,613,258, to provide longitudinally extending channels on the underside of a papermaking felt for the purpose of improving the expressing of water from the felt. In the Jamieson patent the channels were formed by extruding spaced parallel extending plastic monofilament onto the underside of the felt to define the channels. Although the channels as formed in the Jamieson felt were satisfactory for the purpose of removing water from the felt, the Jamieson felt was formed endless, and thus the formation of the water expressing channels as taught by Jamieson were not available in a seamed felt that was separated at the seam and thereafter joined at the ends thereof in the use of the felt in a papermaking machine.
As will be set forth hereinafter, the subject invention provides for the use of plastic monofilaments on the underside of a seamed felt to form water expressing channels therein.